It is known that gel compositions for dispersing volatile material may be prepared from many different polymeric resins.
Among these gels, those that are based on super-absorbent polyacrylate polymers are of particular interest and are described in WO 00/24435 or in EP 835666. The super-absorbent gels have the advantage of requiring small quantities of resin and providing an effective release of the active ingredient for a prolonged period of time.
However, the disclosed gels based on the super-absorbent polyacrylate polymers suffer from the disadvantage of having poor mechanical properties. The consequence of which is that the gels can be easily deformed or broken, under a slight mechanical pressure or a slump, with the undesired consequence that the releasing behaviors are altered, by the change of the surface of the gel, or that the gels can spill out of the container.
In order to avoid the above-mentioned problems, it has been proposed to enclose the gel compositions into vapor permeable bags or use mechanically stronger resins such as carrageerians or polyurethanes. However, none of the solutions is satisfactory as, on the one hand, the use of a bag does not prevent the gel from being deformed and changing its releasing properties and, on the other hand, the gels based on carrageenans or polyurethane resins, compared to the polyacrylate based gel, have inferior performance as a consequence of their tighter matrix. Moreover gels based on carrageenans need elevated processing temperatures, obviously a disadvantage when working with volatile compounds.
Therefore there is still a need for gel compositions which can be obtained at room temperature and are capable of having improved mechanical properties and still performing effective release of the active ingredient for a prolonged period of time.